no u dont if you have two ports on your pc or you have interent through usb you can use these. I assume that your comp is connected to the internet if it is then go to control pannel then network and sharing center. Plug in your 360 and a new connection should appear probably local connection 1 or something. Get up the properties tab on the connection with the internet (not the 360) and then go to the sharing tab. Click share this internet connection and select the local area connection that your xbox is on.
Then on the xbox internet properties select ip protcol 4 and make sure obtain ip and dns automatically are ticked.
You now need to make both connections part of a private network so they can share stuff. Next to each connection there should be a link saying customize click on it and then change it to private on both.
It should now work let me know if you have problems!!!